Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit a0f97e06 authored by Sam Ravnborg's avatar Sam Ravnborg
Browse files

kbuild: enable 'make CFLAGS=...' to add additional options to CC 



The variable CFLAGS is a wellknown variable and the usage by
kbuild may result in unexpected behaviour.
On top of that several people over time has asked for a way to
pass in additional flags to gcc.

This patch replace use of CFLAGS with KBUILD_CFLAGS all over the
tree and enabling one to use:
make CFLAGS=...
to specify additional gcc commandline options.

One usecase is when trying to find gcc bugs but other
use cases has been requested too.

Patch was tested on following architectures:
alpha, arm, i386, x86_64, mips, sparc, sparc64, ia64, m68k

Test was simple to do a defconfig build, apply the patch and check
that nothing got rebuild.

Signed-off-by: default avatarSam Ravnborg <sam@ravnborg.org>
parent 9a39e273

Documentation/kbuild/makefiles.txt

+9 −6
Original line number Diff line number Diff line
@@ -294,7 +294,7 @@ more details, with real examples. 




	This variable is necessary because the top Makefile owns the

	variable $(CFLAGS) and uses it for compilation flags for the

	variable $(KBUILD_CFLAGS) and uses it for compilation flags for the

	entire tree.



	$(EXTRA_AFLAGS) is a similar string for per-directory options
@@ -437,6 +437,7 @@ more details, with real examples. 
	-march=pentium-mmx if supported by $(CC), otherwise -march=i586.

	The second argument to cc-option is optional, and if omitted,

	cflags-y will be assigned no value if first option is not supported.

	Note: cc-option uses KBUILD_CFLAGS for $(CC) options



   cc-option-yn

	cc-option-yn is used to check if gcc supports a given option
@@ -452,6 +453,7 @@ more details, with real examples. 
	option. When $(biarch) equals 'y', the expanded variables $(aflags-y)

	and $(cflags-y) will be assigned the values -a32 and -m32,

	respectively.

	Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options



    cc-option-align

	gcc versions >= 3.0 changed the type of options used to specify
@@ -463,10 +465,11 @@ more details, with real examples. 
		cc-option-align = -falign



	Example:

		CFLAGS += $(cc-option-align)-functions=4

		KBUILD_CFLAGS += $(cc-option-align)-functions=4



	In the above example, the option -falign-functions=4 is used for

	gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used.

	Note: cc-option-align uses KBUILD_CFLAGS for $(CC) options



    cc-version

	cc-version returns a numerical version of the $(CC) compiler version.
@@ -825,17 +828,17 @@ When kbuild executes, the following steps are followed (roughly): 
		#arch/sparc64/Makefile

		AFLAGS += -m64 -mcpu=ultrasparc



    CFLAGS		$(CC) compiler flags

    KBUILD_CFLAGS		$(CC) compiler flags



	Default value - see top level Makefile

	Append or modify as required per architecture.



	Often, the CFLAGS variable depends on the configuration.

	Often, the KBUILD_CFLAGS variable depends on the configuration.



	Example:

		#arch/i386/Makefile

		cflags-$(CONFIG_M386) += -march=i386

		CFLAGS += $(cflags-y)

		KBUILD_CFLAGS += $(cflags-y)



	Many arch Makefiles dynamically run the target C compiler to

	probe supported options:
@@ -847,7 +850,7 @@ When kbuild executes, the following steps are followed (roughly): 
						-march=pentium2,-march=i686)

		...

		# Disable unit-at-a-time mode ...

		CFLAGS += $(call cc-option,-fno-unit-at-a-time)

		KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time)

		...

Makefile

+10 −10
Original line number Diff line number Diff line
@@ -320,7 +320,7 @@ LINUXINCLUDE := -Iinclude \ 


CPPFLAGS        := -D__KERNEL__ $(LINUXINCLUDE)



CFLAGS          := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \

KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \

		   -fno-strict-aliasing -fno-common \

		   -Werror-implicit-function-declaration

AFLAGS          := -D__ASSEMBLY__
@@ -335,7 +335,7 @@ export CPP AR NM STRIP OBJCOPY OBJDUMP MAKE AWK GENKSYMS PERL UTS_MACHINE 
export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS



export CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS

export CFLAGS CFLAGS_KERNEL CFLAGS_MODULE

export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE

export AFLAGS AFLAGS_KERNEL AFLAGS_MODULE



# When compiling out-of-tree modules, put MODVERDIR in the module
@@ -492,36 +492,36 @@ endif # $(dot-config) 
all: vmlinux



ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE

CFLAGS		+= -Os

KBUILD_CFLAGS	+= -Os

else

CFLAGS		+= -O2

KBUILD_CFLAGS	+= -O2

endif



include $(srctree)/arch/$(ARCH)/Makefile



ifdef CONFIG_FRAME_POINTER

CFLAGS		+= -fno-omit-frame-pointer -fno-optimize-sibling-calls

KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls

else

CFLAGS		+= -fomit-frame-pointer

KBUILD_CFLAGS	+= -fomit-frame-pointer

endif



ifdef CONFIG_DEBUG_INFO

CFLAGS		+= -g

KBUILD_CFLAGS	+= -g

AFLAGS		+= -gdwarf-2

endif



# Force gcc to behave correct even for buggy distributions

CFLAGS          += $(call cc-option, -fno-stack-protector)

KBUILD_CFLAGS         += $(call cc-option, -fno-stack-protector)



# arch Makefile may override CC so keep this after arch Makefile is included

NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)

CHECKFLAGS     += $(NOSTDINC_FLAGS)



# warn about C99 declaration after statement

CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)

KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)



# disable pointer signed / unsigned warnings in gcc 4.0

CFLAGS += $(call cc-option,-Wno-pointer-sign,)

KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)



# Use --build-id when available.

LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\

arch/alpha/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -84,7 +84,7 @@ endif 
# For TSUNAMI, we must have the assembler not emulate our instructions.

# The same is true for IRONGATE, POLARIS, PYXIS.

# BWX is most important, but we don't really want any emulation ever.

CFLAGS += $(cflags-y) -Wa,-mev6

KBUILD_CFLAGS += $(cflags-y) -Wa,-mev6



head-y := arch/alpha/kernel/head.o

arch/alpha/kernel/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -3,7 +3,7 @@ 
#



extra-y		:= head.o vmlinux.lds

EXTRA_AFLAGS	:= $(CFLAGS)

EXTRA_AFLAGS	:= $(KBUILD_CFLAGS)

EXTRA_CFLAGS	:= -Werror -Wno-sign-compare



obj-y    := entry.o traps.o process.o init_task.o osf_sys.o irq.o \

arch/alpha/lib/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -2,7 +2,7 @@ 
# Makefile for alpha-specific library files..

#



EXTRA_AFLAGS := $(CFLAGS)

EXTRA_AFLAGS := $(KBUILD_CFLAGS)

EXTRA_CFLAGS := -Werror



# Many of these routines have implementations tuned for ev6.